1. Field of the Invention
The present invention relates to a LCD device and more particularly, to a LCD device with rugged, shining, reflective layer.
2. Description of Related Art
LCD devices are usually available in four types: reflective type, transflective type, projective type and transmissive type. Other than reflective type, most LCD devices are transmissive type. The light source of this type mainly depends on the backlight behind the liquid crystal panel to make the LCD visible. Due to limited brightness, the screen becomes blur and invisible when exposed to sunlight directly because the sunlight reflected from the surface of the screen overshadows the images formed on the LCD.
The reflective type LCD doesn't emit light itself but becomes bright by reflecting the light coming into the liquid crystal panel by way of a reflective substrate rather than glowing by itself. Because the elemental principle of brightness of the reflective type LCD is different from that of the transmissive type LCD, the reflective type LCD does not need backlight or build-in illumination. Moreover, the brightness of the reflective type LCD can be provided by external light sources such as artificial light or natural light. Therefore, the brighter the external light source is, the brighter the reflective type LCD is, and the better the reflective type LCD for outdoor use will be. In addition, because less power for reflective type LCD consumes, this LCD device can be lighter, thinner and more energy-saving and more convenient for bright environment.
The conventional reflective type LCDs includes a layer of reflective material, such as Al or Cr, formed over the surface of a bottom substrate, and a rugged or uneven surface is formed for enhancing reflectivity. If a smooth mirror used as a reflective plate is attached to the back inner wall of the manufactured liquid crystal cell, an observer may look at his/her own image on the LCD panel. This is called “mirror reflective phenomenon.” If the pattern over the reflective plate is in a shape of regular concave and convex wave, the reflected light will be in various colors even though the incident light is white. The surface of the reflective plate resembles the diffraction grating of a spectrometer and produces the same phenomenon. To solve the problem, i.e. to avoid the associated phenomenon of the reflective angle and the wavelength, the surface of the reflective plate is required to be irregularly roughened. The reflective light then includes concurrently positive reflective light and diffused reflective light.
Doriguzzi et al., in U.S. Pat. No. 4,106,859, disclosed a method for manufacturing a rugged surface of an organic layer, particularly a casting method. An even organic layer 120 is roughened under pressure P with a rugged grooved mold 110 to form an irregular surface as shown in FIG. 1a; or as shown in FIG. 1b, an even organic layer 120 is roughened by a cylindrical mold 130 with rugged surface via rolling to provide an irregular surface. Other than the method of casting, Komatsubara et. al. in U.S. Pat. No. 4,519,678 disclosed another method, comprising: forming a projection pattern 210 over a substrate 200; applying a polymer resin layer 220 and a reflective metal film 230 on the projection pattern and the substrate. As shown in FIG. 2, a metal film with rugged surface is thus completed. In addition, Oh et. al. in U.S. Pat. Ser. No. 5,917,567 disclosed yet another method for forming a rugged surface, as shown in FIG. 3a-c. First, a plurality of spacers 321 and a polymer solution 322 are sufficiently mixed. Then, a thin layer of the polymer solution 322 containing the spacers 321 is applied on a substrate 320 by spin coating, and baked to form a thin layer of rough surface. The pixel electrode 324 with reflective character, made of material such as Al or Ag, is formed thereon by sputtering. This results in pixel electrode 324 with rugged surface. Alternatively, prior to a polymer solution 322 being distributed and baked to form a rough surface, a plurality of spacers 321 may be deposited over the substrate 320 first.
However, the foregoing methods require mechanical casting or the presence of spacers to form a rough surface. A reflective metal film cannot be formed unless a rough surface is formed first. They all involve tedious procedures and are not ideal for mass production. Surely one single step for forming a reflective metal film with rough surface will dramatically reduces the time and labor cost for the production.